Starting kelay ctecutt for fluores



March. 6,19 R. F. HAYS, JR I 2,313,744 I STARTING' RELAY CIRCUIT FOR FLUORESCE NT- LAIPS Filed Oct. 10, 1340 www- ATfORNEY Patented Mar.16, 1943 2,313,144 s'raa'rmc RELAY cnwurr For. FLUORES- cnu'r LAMPS Robert F. Hays, .lr., Bloomfield, N. 3., assignor to Westinghouse Electric 8: Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 10, 1940, Serial No. 360,529

6 Claims.

The present invention relates to gaseous discharge lamps and particularly to a time delay relay and circuit for starting and operating such of the lamp. electrodes,

lamps, especially those having at least one filamentary electrode adapted to be preheated to an electron-emitting temperature, such for example as what are now known to the art as fluorescent lamps.

lamp. During the time that the filamentary electrodes of the lamp are being heated to electron-emissive temperature, the current is also flowing through the heater element so that the bimetallic element is heated at approximately the same time that the filamentary electrodes are heated to electron-emissive temprature, with the result that the contacts of the device open to interrupt the series heating circuit for the electrodes and initiate a discharge in the lamp.

Such an arrangement has the disadvantage that thedischarge current for the lamp must flow through the heater'element during entire operation of the lamp in order to maintain the bimetallic element heated and the contacts separated. Moreover, this type of thermalrelay is not operable over a wide range of line voltage fluctuations and the heater element must necessarily be of a constant resistance and designed for one value of current to prevent its burning out.

Since the constant resistance of the heater is not the same as the filamentary electrodes of the lamp, inasmuch as the latter has a positive temperature coemcient of resistance, thereby causing a, change of resistance with temperature, a thermal relay of this type cannot be designed for a wide variation of current so that operation thereof is delayed until the filamentary elecfor too long a period, resulting in overheating In order to eliminate the disadvantages of the above noted type or thermal relay, a glow switch is now in common use. Such type of glow switch is shown and described in Patent 2,200,443, issued March 14, 1940, to E. C. Dench, and assigned to the same assignee as the present invention. Such glow switch possesses the advantageous feature that it consumes no energy during operation of the lamp and is very positive in its operation over a long period of life.

Althoughsuch glow switch operates very satisfactorily for low wattage lamps, it possesses the disadvantage that it does not produce a sufficient time delay for heating the filamentary electrodes of higher wattage lamps, since upon operation its contacts do not remain closed sufficiently long to enable the electron-emitting temperature of the filamentary lamp electrode to reach its optimum temperature.

It is accordingly an object of the present invention to provide a time delay relay for starting a gaseous discharge lamp of the fluorescent type wherein the filamentary electrode of the lamp is preheated to optimum electron-emissive temperature prior to the initiation of a discharge in the lamp.

Another object of the present invention is the provision of a starting circuit for a gaseous discharge lamp of the fluorescent type having a filamentary electrode and wherein a starting relay is employed which has a suiiicient time delay to enable the filamentary electrode of the lamp to be preheated to an optimum electron-emitting temperature.

Another object of the present invention is the provision of a starting circuit for a gaseous distrodes of the lamp reach optimum operating temperature. This is because a low current will not adequately heat the lamp electrodes to optimum temperature while at the same time the heater element is heated suillciently to interrupt the heating circuit. On the other hand, if current is high and the lamp electrodes are heated to optimum temperature, then the heater element causes the heating circuit to remain closed 55 charge lamp of the fluorescent type having a filamentary electrode and wherein a starting relay is employed which has a sufilcient time delay to enable the filamentaryelectrode of the lamp to be preheated to an optimum electronemitting temperature, regardless of wide variations in current range.

lamp having at least one filamentary electrode adapted to be preheated to an optimum .electron-emitting temperature wherein the relay can be readily inserted in a socket and connected' so as to complete a series heating circuit for the filamentary electrode, and is operable with a sufllclent time delay so as to preheat the filamentary electrode to optimum electron-emitting temperature over a wide current range.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

Fig. 1 is a diagrammatic illustration of an electrical circuit for starting and operating a gaseous electric discharge lamp and employing a time delay relay in accordance with the present invention.

Fig. 2 is an elevational view of the elements of the time delay relay itself with some of the elements being shown diagrammatically.

Fig. 3 is an elevational view of a modification of one of the elements of the time delay relay of the present invention.

Fig. 4 is a sectional view taken on the line IVIV of Fig. 3.

Fig. 5 is still another modification of one of the elements of the time delay relay of the present invention.

Fig. 6 is a sectional view taken on the line VI-VI of Fig. 5.

Referring now to the drawing in detail, a gaseous electric discharge device, such as a fiuorescent lamp 5, is shown in Fig. 1 which is provided with oppositely disposed filamentary electrodes 6 and 'I of a refractory metal, such as tungsten or the like, in the form of a coiled coil coated with an electron-emissive material, such as an oxide of barium, strontium or the like, to provide a copious fiow of electrons when heated to an optimum temperature.

After evacuation the lamp is filled with a rare gas at a few millimeters pressure to facilitate starting, to which is added a few drops of mercury. As shown in Fig. 1, one terminal of the electrode 6 is connected by a conductor I through an impedance element in the form of an inductance 9 to one side of the source of supply of the customary domestic potential of 115-230 volts. Likewise, one terminal of the electrode 1 is connected by a conductor ll and switch I! to the opposite side of the domestic source of supply. The remaining terminal of each electrode is connected together through the medium of a time delay relay so that upon operation thereof the electrodes land-l of the lamp 5 are in series with each other and the source of supply, whereby the electrodes are preheated to an optimum electron-emitting temperature.

when the temperature of the electrodes reaches this optimum temperature, the time delay relay operates to interrupt the series heating circuit for the filamentary electrodes, thus causing a discharge therebetweenwith the time delay relay being shunted from the circuit and consuming no energy during operation of the lamp.

The system thus far described differs very little from the circuits of the prior art above noted, with the exception of the construction and operation of the time delay relay device It. The

auxiliary discharge device it as shown in Fig. 1

comprises a casing it provided with a pair of terminals i5 readily enzageable in an appropriate socket so as to connect the time delay relay II in a series heating circuit as shown.

By reference more particularly to Fig. 2, the various elements contained within the casing ll comprise a glow switch it and what will be hereinafter termed a thermal device iI together with a radio frequency suppressing capacitor ll. Theglowswitch llisof thetypeshown and described in the above-mentioned Patent 2,200,443

,andisprovidedwithapairofelectrodeslland 2|, the latter of which is a bimetallic element provided with an electron-emissive material 2!. An ionizable medium, such as neon, argon or helium or a mixture thereof, at a pressure of approximately 75 to millimeters, is disposed in the switch, and upon the application of a potentialtothe electrodes,thegsseousfillingis ionized, causing a glow discharge between the electrodes.

Duetothisrelativelyhighpressureasflbstantial current flows during the discharge which heats the bimetallic electrode 2. with the ruult that it very rapidly deflects into engagement with the other electrode II to extinguish the discharge and at the same time complete the series circuit for the electrodes of the lamp. After the bimetallic electrode 2| cools, it returns to its normal spaced relation relative to the electrode ll. As previously mentioned, this glow switch operates very satisfactorily for lamps ranging in wattage up to approximately 30 watts since the time of engagement of the electrodes is adequate to heat the filamentary electrodes of the lamp to optimum electron-emitting temperature. However, filamentary electrodes of higher wattage lamps require more time for preheating; and the damage caused by inadequate electrode heating is much greater in such higher wattage lamps than in the case of smaller lamps because of resulting electrode sputtering.

Thus it is essential in hlsher wattage lamps toallowthefilamentaryelectrodesto beheated to an optimum temperature entirely independent of line voltage fluctuations or circuit characteristics in order that a discharge be initiated .in the lamp following initial operation of the relay. To insure heating of the filamentary electrodes t and I to the optimum electron-emitting temperature independent of line voltage iiucm tions and circuit characteristics, the time delay relay of the present invention includes the thermal device I! which comprises an envelope provided with a gaseous medium such as helium at a pressure substantially lower than the pressure of the medium within the glow switch it of about 5 millimeters. This thermal device is provided withapairofnormallyclosed contactsiland 2|, the latter of which is a bimetallic element. In addition, a resistance heater element in the form ofatungsteniilament llisdlsposedinthethermaldeviceadiscenttheelectrodelflwhichresistance heater element has substantially the same thermal and electrical characteristics as that of the filamentary electrodes I and I.

AswillbenotedfromllgJ, thethermaldevice I"! is in electrical series with the glow switch It through a connection 28, with the entire time delay relay I! being connected in the circuit so as to form a series heating circuit for the electrodes, as previously mentioned. In addition, the radio frequency suppressing capacitor II is connected in parallel with the electrodes of the glow switch I so as to absorb radiations of radio frequency to prevent interference with radio recep'tion.

Upon closure of the switch I! the voltage of the source of supply is impressed upon the electrodes II and II, of the glow switch it which extends from the som-ce of supply through the inductance I, conductor 8. filamentary electrode ioi'thelamp Landthroughtheterminal llto the. electrode II. and also through the switch it, conductor I I,

ingly heated very rapidly and, as above mentioned, is deflected into engagement with the electrode l9. The series heating circuit for the filamentary electrodes and lot the lamp 5 is interrupt it, with the result that the glow switch accordingly completed. When the electrodes l9 7 and engage each other, the glow discharge is thereby extinguished. The electrode 20 is so designed that the FR effect is such that the fiow of current in the heating circuit for filamentary electrodes 6 and l is sufilcient to maintain the electrode 20 of the glow switch in a heated condition so that the electrodes l9 and 20 are maintained in engagement with each other.

Closure of the heating circuit not only heats the filamentary electrodes 8 and l, but since the resistance heater element is likewise in series in said circuit and has the same thermal and electrical characteristics as the filamentary electrodes, it is likewise simultaneously heated. Consequently, by the time the filamentary electrodes 6 and I of the lamp 5 have reached optimum electron-emitting temperature, the resistance heating element 25 will likewise be heated to a temperature sufiicieht to cause the bimetallic contact 24 of the thermal device I! to be heated,

, lamp 5 fails for any reason to start.

causing deflection thereof and separation from the contact 23.

This interrupts the heating circuit for the filamentary electrodes 6 and l and since the gas pressure in the thermal device I! is very low, no arcing between the contacts 23 and 24 occurs, and such low gas pressure at the same time permits a high transient voltage surge from the inductance}! which initiates a discharge between the electrodes 6 and l of the lamp 5. During operation of the lamp 5 the time delay relay l3 consumes no energy from the source of supply, despite the fact that the contacts 23 and 24 again assume their normally closed position upon cooling of the bimetallic contact 24 and resistance heater element 25, and that the electrodes l9 and 20 likewise assume their normally open position upon cooling of the bimetallic electrode 20, because the voltage impressed across the electrodes l8 and 20 during operation of the lamp 5 is insufllcient to again initiate a discharge in the glow switch I6.

The time delay relay of the present invention eliminates an inherent defect existent in glow switches of the type hereinbefore mentioned. For example, when a glow switch alone such as I5 is used for starting a lamp, the glow switch that the electrical characteristics of the glow switch are altered and the-switch may be inoperative.. Since'the condenser must withstand the high voltage surge, it must necessarily be of a high quality and therefore expensive.

glow switch only closes the circuit and does not contacts and the radio frequency suppressing condenser are not subjected to the high voltage surges, so that the defects above mentioned are eliminated. Moreover, since the glow switch does not interrupt the flow Of current, arcing of the glow switch contacts is eliminated and the longevity thereof is considerably improved.

A further important feature of the present invention resides in the fact that the thermal device ll forming a part of the time delay relay operates as a protective device in the event the For example, when the bimetallic contact 24 i heated, it separates to permit a high voltage surge, as above noted. Since this also interrupts the heating circuit, the heater 25 as well as the electrodes 6 and l of the lamp 5 will naturally cool. Upon reclosure of contacts 23 and 24 if the lamp does not start, the heating circuit is again closed and the contacts operate through the same cycle. However, once the bimetallic contact 24 is heated, it will remain in the open condition the greater portion of the time, with closure thereof approximating only 10% of the time, thus preventing excessive heating of the auxiliary circuit elements such as the impedance element 9.

In Figs. 3 and 4 a modification of the thermal device I1 is shown which differs from that of Fig. 2 in that in lieu of a. resistance heater element in the form of a tungsten filament 25, a high resistance element 21 of silicon, carbon or the like, is carried by the bimetallic contact 24 which engages the contact 23. Again, the operation of the thermal device is identical to that previously described'in. connection with the modification shown in Fig. 2, and the thermal charitself is so designed that its resistance is such Inthe present invention, as above noted,, the' that the flow of current therethrough heats the same to a temperature sufiicient to cause separation of the contacts only after the filamentary electrodes 6 and I reach their optimum electronemitting temperature.

It thus becomes obvious to those skilled in the art that a time delay relay device is herein provided which is particularly adaptable to the starting of fluorescent lamps. Moreover, such time delay relay is so designed that its operation is entirely independent of line voltage fluctuations or circuit characteristics because the same current which heats the filamentary electrodes of the lamp also heats one of the elements of the time delay relay, which insures adequate preheating of the filamentary electrodes to their optimum electron-emitting temperature prior to operation of -the circuit opening element of the time delay switch. By the provision of a time delay relay insuring preheating of the filamentary lamp electrodes to optimum electron-emitting temperature, the initiation of a discharge between the electrodes invariably occurs without sputtering of thelamp electrodes, following initial operation of the time delay relay, with attendant high voltage surge which eliminates any necessity for repetition of its cycle of operation.

Although several embodiments oi the present invention have been shown and described, it is to be understood that other modifications thereof may be made without departing from the spirit and scope of the appended claims.

I claim:

1. A time delay relay for starting a gaseous electric discharge lamp having at least one filamentary electrode adapted to be preheated to an optimum electron-emitting temperature comprising a glow switch and a thermal device adapted to be connected in electrical series relation with each other and in a heating circuit for the electrode of said lamp, said glow switch being operable to close the heating circuit for said electrode upon the application of a potential thereto, and said thermal device having a pair of contacts normally closed prior to initiation of a discharge in saidllamp and operable to open following operation of said glow switch and provided with a heater element connected in series with said glow switch and the normally closed contacts of said thermal device and having preselected characteristics for heating said contacts simultaneously with the heating of said electrode to optimum electron-emitting temperature to cause opening of said contacts and interruption of the heating circuit for said electrode and said heater element with attendant initiation of a,

discharge in said lamp.

2. A time delay relay ior starting a gaseous electric discharge lamp having at least oneflla mentary electrode adapted to be preheated to an optimum electron-emitting temperature comprising a casing provided with terminals for connecting said relay in a heating circuit ior the electrode of said lamp, a glow switch in said casing adapted to close the heating circuit for said electrode upon the applicationoi a potential thereto, and a thermal device in said'casing having a pair of contacts normally closed prior to initiation of a discharge in said lamp and included in the heating circuit for said electrode upon operation of said glow switch and provided with a heater element connected in series with said glow switch and the'normally closed contacts of said thermal device and having preselected characteristics for heating said contacts simultaneously with the heating of said electrode to optimum electron-emitting temperature.

to cause opening of said contacts and interruption of the heating circuit for said electrode and 7 element having preselected characteristics and provided with a heater element connected in series with said glow switch and the normally said heater element with attendant initiation oi a discharge in said lamp.

3. A time delay relay ior starting a gaseous electric discharge lamp having at least one illsmentary electrodeadapted to be preheated to an optimum electron-emitting temperature comprising a glow switch operable to close a heating circuit ior the filamentary electrodeoi said lamp and provided with a pair of normally spaced electrodes therein, an ionizable medium in said tube at a pressure sufficiently high to cause rapid closure of the spaced electrodes upon the application oi a potential thereto, and one'oi said electrodes being a bimetallic element initially heated by the discharge to cause engagement oi closed contacts of said thermal device and ior heating said bimetallic elementsimultaneously with the heating of said filamentary electrode to optimum electron emissivity to cause opening of said contacts and interruption of the heating circuit for said electrode and said heater element, and a gaseous medium in said thermal device at a pressure substantially less than that in said glow switch to enable the passage oi a high transient voltage for initiating a discharge in said lamp at the instant of interruption of the heating circuit by opening of the contacts of said thermal device. I

4. A starting relay for discharge lamps oi the fluorescent type comprising a casing provided with contacts engageable with a socket, a glow switch disposed in said casing and having normally separated contacts adapted to close upon the occurrence of the glow discharge in said glow switch, and a thermal switch disposed in said casing having a heat-responsive element and provided with an electric heater operable by closure of the contacts of said glow switch to cause heating of said heat-responsive element with attendant operation thereoi after the lapse oi a predetermined period of time to interrupt current flow through said glow switch.

5. A starting relay for completing a circuit to a discharge lamp oi the fluorescent type comprising a casing, a glow switch disposed in said casing and having normally separated contacts adapted to close the circuit to said lamp upon the occurrence of a glow discharge in said glow switch, and a thermal switch having a heat-responsive element andv an electric heater operativeiy included in said circuit the'contacts oi said glow switch and said heater being operable to heat said heat-responsive element and cause the latter to interrupt the circuit to said lamp aiterihe lapse oi a predetermined period oi time.

. 6. A starting relay ior completing a circuit to a discharge lamp of the fluorescent type comprising a casing. a slow switch disposed in said casing and having normally separated contacts adapted to close the circuit to said lamp upon the occurrence oi a glow discharge in said glow switch, and a thermal switch having a heat-responsive element and an electric heater operatively included in said circuit upon closure of the contacts of said glow switch and said heater-being operable to heat said heat-responsive element with attendant operation thereof after the lapse oi a predetermined period oi time to interrupt current flow through said glow switch..

ROBERT I". HAYS, JR.

upon, closure oi 

